The US and Russia hold some 95 per cent of the world's nuclear arms

Rachel Courtland, reporter

After almost a year of negotiation, the US and Russia have finally settled on a plan to further reduce their vast nuclear arsenals. If the new agreement is approved, the number of deployed warheads by will be cut by 30 per cent over previous targets. But an ongoing dispute over a European missile defence shield has the potential to scupper the plans.

The US and Russia hold some 95 per cent of the world's nuclear arms, including an estimated 4700 deployed nuclear warheads. The new agreement – a follow-up to the 1991 Strategic Arms Reduction Treaty (START) – would cut the number to 1550 warheads per country over the course of seven years.

The significance of the new agreement is largely symbolic. A fraction of those warheads could still assure mutual destruction, Vanity Fair notes.

But US president Barack Obama and Russian president Dmitry Medvedev hope the new START will show other nations that the world's nuclear superpowers are serious about disarmament. A review of the Nuclear Non-Proliferation Treaty, which has met with faltering support, will be hosted by the US in May.

The US Senate and Russia's Duma must ratify the new START treaty before it can take effect. But this may prove difficult, as some American legislators have expressed concern over Russia's attitude toward the treaty.

While the two countries have agreed on a new plan for offensive weapons, they differ on the subject of missile defence. The US hopes to install a shield of interceptor missiles in Europe to protect against potential attacks from countries like Iran.

Russia suspects the shield is really there to block its own missiles, and in a separate, nonbinding statement has declared it reserves the right to withdraw from START if US missile defence plans seem to threaten its national security, the New York Times reports.

A five-point The Ocean Manifesto plan

High-tech geoengineering might one day just be able to return atmospheric carbon dioxide to below 350 parts per million, at which level coral reefs can persist. But long before then the multiplying effects of changing climate and human pressure will have crippled marine ecosystems. For the ocean to survive, we need to throw it five lifelines by doing the following:

1: Establishing marine reserves

Less than 0.01 per cent of the ocean lies within reserves, but reserves do work: they boost biomass and biodiversity and allow ecosystems to grow resilient. Around the British-controlled Chagos Islands in the Indian Ocean, for example, the seas are not part of a formal reserve but have effectively been protected since 1965 by the presence of the US base at Diego Garcia; reefs here have been able to recover quickly from bleaching events.

2: Ending the freedom of the seas

Only by zoning and controlling access to the ocean can it be rescued. The present situation has led to a depletion of the ocean’s biomass, something which is as important as biodiversity for the resilience of ecosystems. For instance, 95 per cent of filter-feeders have been removed from the ocean. The North Sea and our estuaries once had clear waters full of oyster beds; restoring even a fraction of these will lead to cleaner water and an increase in sunlight for seabed organisms.

3: Controlling fishing fleets

The fishing industry is destroying essential biodiversity and biomass because of huge subsidies and overcapacity. Ending both will mean more fish in the sea as well as on the plate, while cutting the amount of fuel used to catch them.

4: Banning bottom trawling

A widespread ban would allow seabed habitats to recover. The hidden complexity of seabed life is a key component of the ocean’s ability to recycle nutrients.

5: Controlling pollution

Agricultural fertilisers being washed into rivers are a major cause of the growth in deoxygenated dead zones in coastal waters worldwide, and plastics are pulling poisons into food webs.